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ICD-10 Guide
DiagnosesAnkylosing Spondylitis

Ankylosing Spondylitis

ICD-10 Coding for Ankylosing Spondylitis(M45.0, M45.6)

PRIMARY SPECIALTYRheumatology
COMPLEXITYHigh
LAST UPDATED09/15/2025
Sam Tuffun, PT, DPT
Physical Therapist | Medical Coding & Billing Contributor

Diagnosis Overview

What is Ankylosing Spondylitis?
Essential facts and insights about Ankylosing Spondylitis

Key Clinical Considerations:

  • Chronic inflammatory back pain lasting more than 3 months, typically worse in the morning and improves with activity.
  • Positive HLA-B27 antigen test in some patients, although not all individuals with ankylosing spondylitis will test positive.
  • Limited spinal mobility and chest expansion during physical examination.
  • Imaging findings such as sacroiliitis on X-rays or MRI, showing inflammation of the sacroiliac joints.
  • Severity criteria include the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) for assessing disease activity.

Clinical Information

Clinical Criteria & Documentation Requirements

  • Complete medical history including onset, duration, and characteristics of symptoms.
  • Specific terminology such as 'sacroiliitis', 'spinal stiffness', and 'HLA-B27 positive' must be documented.
  • Examples include noting the degree of spinal mobility and any imaging results that support the diagnosis.
  • Documentation must demonstrate medical necessity for treatments prescribed, including physical therapy or medications.
  • Quality measures may include tracking disease activity and functional status over time.

Coding Guidelines

Usage Guidelines & Examples

  • Use M45.0 for ankylosing spondylitis of the lumbar spine and M45.6 for other specified sites.
  • Do not use these codes for non-inflammatory back pain or other types of spondyloarthritis without proper documentation.
  • Related codes include M46.0 for other spondylopathies and M05 for inflammatory polyarthropathies.
  • Common errors include misclassifying the type of spondyloarthritis or failing to document the specific site of involvement.
  • In complex cases, ensure to document all relevant clinical findings and consider additional codes for associated conditions.

Code Exclusions

Important Exclusions

  • Excludes non-radiographic axial spondyloarthritis (M46.9) and other forms of spondyloarthritis.
  • Alternative codes for excluded conditions include M54.5 for low back pain.
  • Conditions are excluded to ensure accurate representation of inflammatory spondyloarthritis.
  • Common mistakes include using M45 codes for mechanical back pain or other non-inflammatory conditions.
  • Related but distinct conditions include psoriatic arthritis and reactive arthritis.

Related ICD-10 Codes

Primary Codes
M45.0
Ankylosing spondylitis of lumbar spine
M45.6
Ankylosing spondylitis, other site
Ancillary Codes
H20.1
Differential Codes
M46.8
M53.3

Related CPT Codes

CPT codes will be available in a future update.

Specialty Focus

Primary Specialty

Rheumatology

Specialty Applications

  • Patients diagnosed with ankylosing spondylitis, often presenting in young adults.
  • Higher prevalence in males, typically diagnosed between ages 15-45.
  • Clinical settings include outpatient rheumatology clinics and inpatient care for severe cases.
  • Specialty-specific applications in rheumatology and physical medicine.
  • Treatment contexts include management of chronic pain and physical therapy interventions.

Coding Complexity

High Complexity

This diagnosis requires careful attention to:

  • Comprehensive clinical documentation
  • Accurate code selection based on clinical criteria
  • Proper exclusion considerations
  • Specialty-specific coding guidelines

Documentation

Documentation Templates

Template 1

Template: 'Patient diagnosed with ankylosing spondylitis based on chronic inflammatory back pain and imaging findings.'

Template 2

Template: 'Clinical presentation consistent with ankylosing spondylitis including limited spinal mobility and positive HLA-B27.'

Template 3

Template: 'Diagnostic criteria met as evidenced by MRI showing sacroiliitis and patient-reported symptoms.'

Template 4

Template: 'Treatment plan initiated for ankylosing spondylitis with physical therapy and NSAIDs.'

Template 5

Template: 'Follow-up care for ankylosing spondylitis including monitoring of disease activity and functional status.'

Billing Information

Billing Considerations

  • Ensure proper documentation for billing
  • Verify code specificity requirements
  • Check for any additional codes needed
  • Review payer-specific guidelines

Common Issues

  • Insufficient clinical documentation
  • Incorrect code selection
  • Missing supporting diagnoses
  • Timing and frequency documentation

Frequently Asked Questions

What documentation is required for this diagnosis?

Documentation must include clinical findings, imaging results, and symptom duration.

How does this differ from similar diagnoses?

Ankylosing spondylitis is characterized by specific inflammatory changes in the spine and sacroiliac joints.

What are common billing considerations?

Ensure that the diagnosis is supported by clinical documentation to optimize reimbursement.

What procedures are typically associated?

CPT codes for physical therapy, imaging studies, and laboratory tests may be relevant.

Are there any quality reporting implications?

Quality measures may include tracking disease activity and functional outcomes in patients.